JP3116742B2 - Continuous casting apparatus and continuous casting method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a continuous casting apparatus and a casting method capable of making the flow of molten steel in a continuous casting mold near the surface of molten steel uniform and improving the quality of a slab.

[0002]

2. Description of the Related Art In order to improve the quality of a slab in continuous casting of steel, it is necessary to appropriately suppress the flow of molten steel in a mold, to suppress the occurrence of entrainment of powder for continuous casting into molten steel, and to improve the initial solidification shell. It is necessary to prevent inclusion of inclusions and to make the thickness of the solidified shell uniform.

[0003] The powder for continuous casting is used as a lubricant between a mold and a slab. When the powder is entrained in molten steel due to excessive flow of molten steel, a slag bite or the like is generated, and the slab is cast. Degrades the quality of Fluctuations in the molten metal level locally change the amount of powder flowing as a lubricant between the mold and the slab, causing uneven thickness of the solidified shell.

[0004] On the other hand, when stagnation occurs in the flow of molten steel in the mold, the temperature of the molten steel in that portion is lowered, the growth of the solidified shell is locally accelerated, and the shell thickness becomes uneven. As a result, a difference occurs in the stress acting on the slab, and a vertical crack is generated.

[0005] It will be explained in more detail that such defects of the slab are deeply related to the flow phenomenon of the molten steel in the mold.
That is, a refractory nozzle immersed in the molten steel is used to inject the molten steel into the mold, but due to the discharge flow from the immersion nozzle, the flow of the molten steel in the mold becomes irregular, and the flow velocity is not constant. As a result, the surface of the molten steel (hereinafter referred to as the molten metal surface) is wavy and fluctuates up and down, so that the molten metal surface temperature is not uniform in the mold and the thickness of a part of the molten powder layer existing on the molten metal surface is reduced. Or a portion where the molten powder layer itself disappears occurs.

[0006] As a result, the unmelted powder present on the molten powder layer comes into contact with the molten steel, and the frequency of being caught and trapped in the molten steel increases, resulting in slagging flaws. In addition, when the molten metal level fluctuates, the amount of molten powder flowing between the slab and the mold locally changes, and the amount of heat transferred from the molten steel to the mold is not uniform. This leads to cracks.

The situation of the conventional continuous casting as described above will be described with reference to FIG.

FIG. 3 is a longitudinal sectional view schematically showing the flow of molten steel in a mold in the conventional continuous casting. When the molten steel 3 is injected from the immersion nozzle 2 into the mold 1, the molten steel flow colliding with the mold short side wall 1 a side of the mold 1 becomes an upward flow toward the molten metal surface and a downward flow toward the lower side of the mold 1. Split. The upward flow raises the level of the molten metal near the short side wall 1a of the mold as shown in FIG. For this reason, the thickness of the molten powder layer 9 becomes smaller at the rising position of the molten metal surface and becomes larger at the falling position of the molten metal surface as shown in the figure. When the casting speed is increased to improve the productivity, the discharge flow velocity from the immersion nozzle 2 increases, and the upward flow velocity of the molten steel 3 also increases. For this reason, the amount of swelling of the molten metal surface increases, and the undulation and vertical fluctuation of the molten metal surface also increase. Due to such a phenomenon, unmelted powder is rolled into molten steel, and the thickness of the solidified shell 4 fluctuates or becomes non-uniform. It becomes.

As a method for improving the quality of a slab, Japanese Patent Application Laid-Open No. 5-55220 discloses a continuous casting method using a static magnetic field and a mold thereof. In this method, a static magnetic field is generated between each pair of upper and lower magnetic poles provided on each back surface of the opposite side wall of the mold, and the intensity of the static magnetic field generated between one magnetic pole is made smaller or larger than that of the other, The damping is applied to the molten steel flow supplied from the immersion nozzle into the mold. Thereby, braking can be applied to the upward flow and the downward flow generated when the discharge flow from the immersion nozzle collides with the short side wall of the mold, and the above-described downward flow causes deep inclusion of the inclusion into the molten steel or hot water. As a result of suppressing the surface fluctuation and the non-uniformity of the temperature, the melting of the powder for continuous casting is not hindered, so that it is possible to produce a high quality cast slab with high efficiency.

[0010]

However, the method of the present invention has the following problems. That is, when a static magnetic field is applied to the molten steel flow in the mold, a force acts in the direction opposite to the direction of the molten steel flow, so the molten steel flow velocity in the static magnetic field application region decreases,
Since the braking force does not act on the molten steel flowing outside the static magnetic field application area in the direction of the static magnetic field application area, the molten steel flow attempts to change its direction to the direction without the static magnetic field, and the discharge flow from the immersion nozzle moves up and down the mold. Narrowed by the static magnetic field of the magnetic poles installed in
During this time, the molten steel flow stagnates.

When the casting speed is constant, the discharge flow from the immersion nozzle is also constant, so that the discharge flow enters the stagnant region of the molten steel flow sandwiched by the static magnetic field. Becomes extremely unstable. Because of this, inclusions are caught in the molten steel by the discharge flow from the immersion nozzle and are caught by the solidified shell, or the molten metal surface fluctuates sharply, so that the powder is caught in the molten steel,
A slab defect occurs.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to disperse a molten steel flow over the entire surface of a molten metal in a mold so that the molten steel flow can be changed without causing a stagnation area. It is an object of the present invention to provide a continuous casting apparatus and a casting method capable of producing a cast slab of excellent quality while suppressing the occurrence of slabs.

[0013]

The gist of the present invention is as follows.
There is a continuous casting apparatus of (1) and a method using this apparatus of (2).

(1) A continuous casting apparatus in which one electromagnet is opposed to both long side walls of a continuous casting mold having a rectangular horizontal cross section. The electromagnet surrounds a plurality of iron cores. Consisting of one coil, the distance between the plurality of iron cores and the outer surface of the mold wall can be adjusted independently for each iron core, and the installation positions of the plurality of iron cores are equivalent to the level of the molten steel surface in the mold and the immersion nozzle. A continuous casting apparatus characterized by being at a level equivalent to the depth of immersion in molten steel in a mold.

(2) By using the apparatus of (1) above, by increasing the distance between the iron core at the center of the long side wall of the mold and the outer surface of the mold wall, the magnetic field intensity in the mold at the center of the long side wall of the mold is increased. Continuous casting method characterized in that casting is performed with a small size.

[0016]

The continuous casting apparatus according to the present invention will be described with reference to FIGS. FIG. 1 is a partial side view and a partial vertical cross-sectional view schematically showing a side face viewed from a long side wall of a mold, and FIG. 2 is a plan view of the side view from above.

An immersion nozzle 2 is fixed to the center of the continuous casting mold 1 so as to have a constant immersion depth, and molten steel 3 is injected into the mold 1 from the immersion nozzle 2. A solidified shell 4 grows from inside the mold 1. In addition, powder (not shown) is put on the surface of the molten steel 3, that is, on the molten metal surface.

Both long mold side walls 1b of the mold 1 shown in FIG.
1, the width direction outside the long side wall 1b of the mold as shown in FIG. 2 within the range between the level corresponding to the molten metal surface in the mold and the level equivalent to the immersion depth of the immersion nozzle 2 as shown in FIG. In addition, a pair of electromagnets each including a plurality of iron cores 5 and a single coil 6 surrounding the plurality of iron cores are provided to face each other.

Each iron core 5 of the electromagnet has a mechanism capable of independently changing the distance d between the iron core 5 and the outer surface of the long side wall 1b. As this mechanism, for example, the following method is preferably used.

A hydraulic cylinder 7 is connected to each iron core 5 of the electromagnet, and the main body of the hydraulic cylinder 7 is fixed to a frame 8 supporting the mold 1. By adjusting the oil pressure and independently changing the length of each hydraulic cylinder rod, the distance d between the iron core 5 and the outer surface of the mold long side wall 1b can be changed for each iron core 5. Here, an example in which the hydraulic cylinder 7 is used has been described, but a control mechanism of the interval d using an air cylinder, a motor drive, or a manual worm gear may be used instead.

With such a mechanism, even when the current flowing through the coil 6 is constant, the distance d is appropriately controlled to locally adjust the magnetic field intensity generated in the mold 1 in accordance with the number of iron cores 5. Can be changed.

As shown in FIG. 1, molten steel 3 is immersed in nozzle 2
When it is injected into the mold 1 from the mold, it collides with the mold short side wall 1a side, and is separated into an upward flow toward the molten metal surface and a downward flow downward the mold. The upward flow is applied with a braking force by a static magnetic field generated by the iron core 5 of the electromagnet, and is dispersed in the direction of the molten metal surface. That is, when a static magnetic field is applied to the vicinity of the molten metal surface and the discharge amount of the molten steel from the immersion nozzle is kept constant, the upward flow due to the collision on the side of the mold short side wall 1a due to the braking force is applied to the entire molten metal surface. Distributed. When the ascending flow is dispersed over the entire surface of the molten metal in this way, the flow velocity of the ascending flow is reduced, the amount of rise of the molten surface is also reduced, the fluctuation of the molten surface is suppressed, and the stagnant region of the molten steel flow is eliminated. The low temperature region of the molten metal surface is eliminated, and the prevention of the decrease of the molten metal surface temperature and the uniformization of the temperature and the viscosity are achieved.

The reason why the position of the iron core 5 in the height direction with respect to the mold 1 is limited between the level corresponding to the molten metal surface in the mold and the level corresponding to the immersion depth of the immersion nozzle 2 is as follows.

That is, when a static magnetic field is applied to the molten steel flow, the flow of the molten steel flows in a direction where there is no static magnetic field due to the action of the braking force acting in the opposite direction to the molten steel flow. Therefore, it is necessary to avoid applying a static magnetic field directly to the discharge flow from the immersion nozzle 2.

At this time, if the distance d between the iron core 5 and the outer surface of the long side wall 1b is further increased at the center of the long side wall 1b near the immersion nozzle 2, the magnetic field intensity is reduced at this portion. As a result, the distribution of the magnetic field strength can be given to the long side wall 1b of the mold, that is, the width direction of the slab. The “central part of the mold long side wall 1b near the immersion nozzle 2” here means, for example, five iron cores 5 provided in FIG.
Of the immersion nozzle 2 near the center. The desirable "center of the mold" is in the range of 10 to 30% with respect to the inner length of the mold long side wall 1b.

As a result, it is possible to suppress a decrease in the flow velocity of the molten steel in the vicinity of the molten metal surface at the center of the mold and to make the flow velocity of the molten steel in the vicinity of the immersion nozzle uniform. This makes it possible to easily eliminate a low-temperature region that tends to occur at the center of the mold.

In the continuous casting apparatus of the present invention, the following effects can be further obtained when the casting speed is increased. That is, since the discharge speed of the molten steel from the immersion nozzle increases as the casting speed increases, the speed of the upward flow generated by colliding with the short side of the mold also increases, and the flow speed in the direction of the immersion nozzle also increases. As described above, since the molten steel flow velocity near the molten metal surface changes depending on the casting speed, it is necessary to control the molten steel flow more strongly by changing the strength of the magnetic field generated by the electromagnet according to the increase in the casting speed. Even in the case where there is such a need, an electromagnet having a plurality of iron cores and one coil is provided facing each other at an appropriate height position outside both long side walls of the mold, and the iron core and the mold length are provided. Distance d to the outer surface of the side wall
, The intensity of the generated magnetic field can be arbitrarily and easily changed, and a desired control of the molten steel flow can be obtained, thereby making it possible to produce a high quality cast slab.

FIGS. 1 and 2 show an example in which the number of iron cores 5 is five on one side, but a desirable number range is 3 to 7 on one side. The desirable range of the magnetic field strength for each iron core 5 is 500 to 3000 Gauss, and the desirable range of the variable distance d is 10 to 300 mm. When changing the magnetic field strength, if the strength at both ends is 100, the magnetic field strength at the center is 20
It is desirable that the magnetic field strength of the iron core between both ends and the center be a value between them.

[0029]

EXAMPLE A continuous casting test of a medium carbon steel slab was conducted under the conditions shown in Tables 1 and 2 using an apparatus having five iron cores as shown in FIG. The incidence was investigated.

[0030]

[Table 1]

[0031]

[Table 2]

The casting conditions other than those indicated were as follows.

Continuous casting machine, number of strands: 1 Mold width (Length on long side): 1250 mm Mold thickness (Length on short side): 250 mm Superheat degree of molten steel in tundish: 10 to 40 ° C Immersion nozzle immersion depth Length: 300mm Coil current: 3000A Surface defects are evaluated by visual observation for total crack length per unit length, and internal defects are evaluated by cutting a slab in a direction perpendicular to the casting direction and visually observing unit length. The total length per unit was measured, and the incidence of the comparative example without the application of a static magnetic field was calculated.
1.0, which was used as the reference value. The results of the survey are shown in Table 1.

As shown in Table 1, when the uniform static magnetic field was applied, the magnetic field intensity became weaker toward the center in the width direction of the mold as compared with the comparative example in which the static magnetic field was not applied. In this case, it becomes better. In particular, Example 3 of the present invention, in which the reduction ratio of the static magnetic field intensity is increased toward the central iron core No. 3, is the most excellent.

[0035]

According to the present invention, a continuous cast slab having few external and internal defects can be obtained.

[Brief description of the drawings]

FIG. 1 is a partial side view and a partial longitudinal sectional view schematically showing a side surface of a continuous casting apparatus of the present invention as viewed from a long side wall of a mold.

FIG. 2 is a plan view of FIG. 1 as viewed from above.

FIG. 3 is a longitudinal sectional view schematically showing the flow of molten steel in a mold in conventional continuous casting.

[Explanation of symbols]

1: Mold, 1a: Mold short side wall, 1b: Mold long side wall, 2:
Immersion nozzle, 3: molten steel, 4: solidified shell, 5: iron core,
6: coil, 7: hydraulic cylinder,
8: frame, 9: molten powder layer

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-6-603 (JP, A) JP-A-4-344858 (JP, A) JP-A-2-284750 (JP, A) JP-A-1- 289550 (JP, A) JP-A-60-72652 (JP, A) JP-A-8-19842 (JP, A) JP-A-6-297093 (JP, A) JP-A-7-9094 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) B22D 11/115 B22D 11/04 311

Claims (2)

(57) [Claims] 1. A continuous casting apparatus in which one electromagnet is opposed to both long side walls of a continuous casting mold having a rectangular horizontal cross section, wherein the electromagnet includes a plurality of iron cores and a plurality of iron cores.
The distance between the multiple iron cores and the outer surface of the mold wall can be adjusted independently for each iron core, and the installation positions of the multiple iron cores are equivalent to the level of the molten steel surface in the mold and the immersion nozzle. A continuous casting apparatus characterized by being at a level equivalent to a immersion depth in molten steel in a mold. 2. The apparatus according to claim 1, wherein the distance between the iron core at the center of the mold long side wall and the outer surface of the mold wall is increased to reduce the magnetic field intensity in the mold at the center of the mold long side wall. A continuous casting method characterized by casting in a small size.